U.S. patent application number 11/392823 was filed with the patent office on 2006-10-05 for etching method and apparatus, computer program and computer readable storage medium.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Atsushi Kawabata, Shinya Morikita.
Application Number | 20060219657 11/392823 |
Document ID | / |
Family ID | 37069057 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060219657 |
Kind Code |
A1 |
Morikita; Shinya ; et
al. |
October 5, 2006 |
Etching method and apparatus, computer program and computer
readable storage medium
Abstract
An etching method, for etching a silicon nitride film on an
underlying silicon oxide film by using a hard mask whose principal
component is a silicon oxide, includes a step of etching the hard
mask by using the resist film as a mask to form a mask pattern
therein; a step of ashing the resist film; a step of oxidizing the
hard mask; a main etching step of etching the silicon nitride film
by using the patterned hard mask as a mask; and a step of
overetching the silicon nitride film at a high selectivity of the
silicon nitride film to the silicon oxide film. The main etching
step is performed after the step of forming the mask pattern in the
hard mask and before the overetching step at a selectivity of the
silicon nitride film to the silicon oxide film smaller than that in
the overetching step.
Inventors: |
Morikita; Shinya;
(Hillsboro, OR) ; Kawabata; Atsushi;
(Nirasaki-shi, JP) |
Correspondence
Address: |
C. IRVIN MCCLELLAND;OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Minato-ku
JP
|
Family ID: |
37069057 |
Appl. No.: |
11/392823 |
Filed: |
March 30, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60666700 |
Mar 31, 2005 |
|
|
|
Current U.S.
Class: |
216/41 ;
156/345.24; 216/59; 216/79; 257/E21.252; 257/E21.256; 257/E21.257;
257/E21.267; 438/706 |
Current CPC
Class: |
H01L 21/31138 20130101;
H01L 21/3143 20130101; H01J 37/32935 20130101; H01L 21/31144
20130101; H01L 21/31116 20130101 |
Class at
Publication: |
216/041 ;
438/706; 216/059; 156/345.24; 216/079 |
International
Class: |
B44C 1/22 20060101
B44C001/22; C23F 1/00 20060101 C23F001/00; H01L 21/306 20060101
H01L021/306; H01L 21/302 20060101 H01L021/302 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2005 |
JP |
2005-097351 |
Claims
1. An etching method for etching a silicon nitride film in a
laminated body wherein the silicon nitride film is laminated on a
silicon oxide film and is covered with a hard mask whose principal
component is a silicon oxide, and a patterned resist film is formed
on the hard mask, the method comprising: (a) an etching step of
etching the hard mask by using the resist film as a mask to form a
mask pattern in the hard mask; (b) an ashing step of ashing the
resist film; (c) an oxidizing step of oxidizing the surface of the
hard mask under a different condition from that in the ashing; (d)
a main etching step of etching the silicon nitride film by using
the patterned hard mask as a mask; and (e) an overetching step of
overetching the silicon nitride film under a selectivity condition
of the silicon nitride film to the silicon oxide film that an
etching of the silicon oxide film exposed under the silicon nitride
film is suppressed, wherein the main etching step (d) is performed
after the step (a) and before the overetching step (e) at a
selectivity of the silicon nitride film to the silicon oxide film
smaller than the selectivity in the overetching step (e).
2. The etching method of claim 1, wherein the main etching step (d)
is performed after the ashing step (b) and before the oxidizing
step (c).
3. The etching method of claim 1, wherein the main etching step (d)
is performed after the step (a) and before the ashing step (b).
4. The etching method of claim 1, wherein the oxidizing step (c) is
performed with a plasma generated by plasmarizing oxygen gas.
5. The etching method of claim 1, wherein the overetching step (e)
is performed with a plasma generated by plasmarizing a gaseous
mixture of a gas containing carbon, fluorine and hydrogen and
oxygen gas.
6. The etching method of claim 1, wherein the thickness of the hard
mask is 50 nm or less.
7. The etching method of claim 1, wherein the thickness of the
silicon oxide film is 5 nm or less.
8. The etching method of claim 1, wherein the thickness of the
silicon nitride film is 50 nm or larger.
9. An apparatus for performing an etching process on a substrate
with a plasma generated by plasmarizing a processing gas, the
apparatus including an aritightly sealed processing chamber having
therein a mounting table on which the substrate is mounted, a unit
for supplying the processing gas into the processing chamber, and a
unit for plasmarizing the processing gas in the processing chamber,
the apparatus comprising: a controller for controlling each of the
units to execute the etching method described in claim 1.
10. A program executed on a computer, the program being used in an
apparatus for etching a substrate by introducing a processing gas
into a processing chamber, wherein the program is configured to
execute the etching method described in claim 1.
11. A computer-readable storage medium storing therein the program
described in claim 10.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an etching method; and,
more particularly, to an etching method and apparatus for etching a
silicon nitride film on an underlying silicon oxide film by using a
hard mask whose principal component is silicon oxide as a mask, a
program for performing the etching method and a computer-readable
storage medium storing the program.
BACKGROUND OF THE INVENTION
[0002] In order to develop high-integration semiconductor devices
with a thinner film structure, the film's kind and structure has
been variously studied, and, for example, new CMOS gate structures
have been proposed. In a conventional CMOS gate structure, a gate
insulating film is formed on a silicon film, and a thinning of the
gate insulating film has been progressed. However, a leakage
current increases as the gate insulating film becomes thinner, so
that the conventional gate structure has a limitation to the
thinning thereof.
[0003] As one of the new CMOS gate structures, there is, e.g., a
so-called three-dimensional gate structure. In such a structure, it
is required to form a gate electrode having a fine and
three-dimensional shape. Further, in an aspect of a material, a
metal gate electrode is under investigation instead of a
conventional polycrystalline silicon electrode, and accordingly,
considerably complex processes are required in a next-generation
semiconductor device manufacturing process.
[0004] As one of the processes, a process for etching a silicon
nitride (SiN) film on an underlying silicon oxide (SiO.sub.2) film
has been studied. The patterned silicon nitride film formed by the
etching is used in forming the gate electrode later.
[0005] However, in general, in case of etching a film, an etching
rate of a substrate surface is not completely uniform, and it is
difficult to make the etching rates of a central portion and a
peripheral portion identical to each other. Accordingly, the
etching is continued after the film is etched to expose an
underlying film, which is called an overetching. Generally, in case
of the overetching, it is required to ensure a high selectivity of
the film to the underlying film, but the selectivity of the film to
the underlying film is approximately 7 to 10 at most.
[0006] However, in a semiconductor device structure being
considered herein, the silicon oxide film as the underlying film is
very thin, e.g., 5 nm. In this case, a high selectivity of, e.g.,
about 20 to 40 is required to perform the overetching. Japanese
Patent Laid-open Application No. 2003-229418 discloses a method for
performing an etching by using, as an etching gas, a gaseous
mixture containing CH.sub.3F gas and O.sub.2 gas wherein the mixing
ratio (O.sub.2/CH.sub.3F) of the O.sub.2 gas to the CH.sub.3F gas
is 4 to 9, in order to increase the selectivity of the silicon
nitride film to the silicon oxide film when etching the silicon
nitride film by using the silicon oxide film as a mask. Therefore,
in the process for etching the silicon nitride film on the
underlying silicon oxide film, by using the gaseous mixture upon
the overetching, it is possible to etch the silicon nitride film
while suppressing the reduction of the underlying film even though
the underlying silicon oxide film is thin.
[0007] However, in case of using the aforementioned gaseous
mixture, there occur problems as described below. FIG. 10A is a
view showing a laminated body before etching the above-described
silicon nitride film, and in FIG. 10A, reference numerals 11, 12,
13, 14 and 15 denote a silicon (Si) film, a silicon oxide film, a
silicon nitride film, a nitrogen containing silicon oxide (SiON)
film serving as a hard mask, a resist film and a resist pattern
formed in the resist film 15, respectively. In case of performing a
conventional etching on such laminated body, the SiON film 14 is
etched by using the resist film 15 as a mask, the resist film 15 is
removed by ashing, and an etching is then performed with the
gaseous mixture described in Japanese Patent Laid-open Application
No. 2003-229418 by using the SiON film 14 as a mask.
[0008] However, as described above, if an etching is performed by
using a gas having a very high selectivity of the silicon nitride
film 13 to the silicon oxide film 12, an etching action to the
silicon nitride film 13 is strong. At this time, since the silicon
nitride film 13 and the SiON film 14 serving as a hard mask have a
similar material composition, the gaseous mixture causes local
damage to the SiON film 14. Further, because the SiON film 14 is
thin, e.g., 50 nm, and the SiON film 14 is not completely uniform
even if it has an in-surface uniformity within a specification,
holes 18 are formed in the SiON film 14 as confirmed by an
experiment. If there occurs such a phenomenon wherein the holes 18
are formed (hereinafter referred to as "pitting"), a surface of the
silicon nitride film 13 is damaged through the holes 18, which
affects a next process.
[0009] It may be considered to protect the SiON film 14 without
ashing the resist film 15 to remain when etching the silicon
nitride film 13. However, because the gaseous mixture contains a
large amount of oxygen, the resist film 15 is ashed when the
silicon nitride film is etched. Therefore, in order to protect the
SiON film 14, a film thickness of the resist film 15 has to be
large. However, in that case, an etching profile is deteriorated.
That is, in order to improve the etching profile, the resist film
15 is required to be thin. Under these circumstances, there is
demanded an etching method capable of performing the
above-described etching without damaging the silicon nitride
film.
[0010] Further, Japanese Patent Laid-open Application No.
2000-269220 discloses, as a method for forming a hard mask of
silicon nitride, a technology capable of thinning a silicon nitride
layer by oxidizing an antireflection film on a silicon nitride
layer by using an oxygen plasma generated when a resist mask
located on the antireflection film is ashed to thereby use the
oxidized antireflection film as a protection layer. However, the
technology cannot achieve the object of the present invention.
SUMMARY OF THE INVENTION
[0011] It is, therefore, an object of the present invention to
provide a technology for etching a silicon nitride film at whose
bottom a silicon oxide film is located, by using a hard mask whose
principal component is silicon oxide as a mask, wherein the silicon
nitride film is not damaged.
[0012] In accordance with an aspect of the present invention, there
is provided an etching method for etching a silicon nitride film in
a laminated body wherein the silicon nitride film is laminated on a
silicon oxide film and is covered with a hard mask whose principal
component is a silicon oxide, and a patterned resist film is formed
on the hard mask, the method including: (a) an etching step of
etching the hard mask by using the resist film as a mask to form a
mask pattern in the hard mask; (b) an ashing step of ashing the
resist film; (c) an oxidizing step of oxidizing the surface of the
hard mask under a different condition from that in the ashing; (d)
a main etching step of etching the silicon nitride film by using
the patterned hard mask as a mask; and (e) an overetching step of
overetching the silicon nitride film under a selectivity condition
of the silicon nitride film to the silicon oxide film that an
etching of the silicon oxide film exposed under the silicon nitride
film is suppressed, wherein the main etching step (d) is performed
after the step (a) and before the overetching step (e) at a
selectivity of the silicon nitride film to the silicon oxide film
smaller than the selectivity in the overetching step (e). In the
present invention, the oxidization of the surface of the hard mask
means that a part thereof is oxidized in the thickness direction
thereof without being oxidized up to the bottom surface of the hard
mask, but does not mean a general surface oxidation where only the
surface thereof is oxidized.
[0013] Preferably, the main etching step (d) is performed after the
ashing step (b) and before the oxidizing step (c) and, more
preferably, the main etching step (d) is performed after the step
(a) and before the ashing step (b). The oxidizing step (c) may be
performed with a plasma generated by plasmarizing oxygen gas, and
the overetching step (e) may be performed with a plasma generated
by plasmarizing a gaseous mixture of a gas containing carbon,
fluorine and hydrogen and oxygen gas.
[0014] Preferably, the thicknesses of the hard mask, the silicon
oxide film and the silicon nitride film are 50 nm or less, 5 nm or
less and 50 nm or larger, respectively.
[0015] In accordance with another aspect of the present invention,
there is provided an apparatus for performing an etching process on
a substrate with a plasma generated by plasmarizing a processing
gas, the apparatus including an aritightly sealed processing
chamber having therein a mounting table on which the substrate is
mounted, a unit for supplying the processing gas into the
processing chamber, and a unit for plasmarizing the processing gas
in the processing chamber, the apparatus including: a controller
for controlling each of the units to execute the etching method
described above.
[0016] In accordance with still another aspect of the present
invention, there is provided a program executed on a computer, the
program being used in an apparatus for etching a substrate by
introducing a processing gas into a processing chamber, wherein the
program is configured to execute the etching method described
above. Further, there is provided a computer-readable storage
medium storing the program described above.
[0017] In accordance with the present invention, in etching the
silicon nitride film which is laminated on a silicon oxide film and
covered with a hard mask whose principal component is a silicon
oxide, after the resist film is ashed, the surface of the hard mask
is oxidized in advance under a different condition from that in the
ashing and the silicon nitride film is overetched at a high
selectivity of the silicon nitride film to the underlying silicon
oxide film. Accordingly, an oxidation film formed on the surface of
the hard mask serves as a protective layer for the hard mask upon
the overetching, so that the damage to the hard mask is suppressed
and occurrence of a pitting is prevented. As a result, it is
possible to perform the etching in a good state without imparting
any damage to the surface of the silicon nitride.
[0018] Further, in case the underlying silicon oxide film is a very
thin film of, e.g., 5 nm or less and the silicon nitride film to be
etched is sufficiently thick compared with the underlying film, it
is necessary to set the selectivity of the silicon nitride film to
the underlying silicon oxide film at a high level, and by dosing
so, the etching action to the hard mask becomes increased. In the
above point of view, it can be said that the etching method of the
present invention is particularly effective in case of a thin hard
mask.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The above and other objects and features of the present
invention will become apparent from the following description of
preferred embodiment given in conjunction with the accompanying
drawings, in which:
[0020] FIG. 1 offers a longitudinal cross-sectional side view
showing an example of an etching apparatus employing an etching
method of the present invention;
[0021] FIGS. 2A to 2C show explanatory views showing a process in
accordance with a first preferred embodiment of the present
invention;
[0022] FIGS. 3A to 3C are explanatory views showing the process in
accordance with the first preferred embodiment of the present
invention;
[0023] FIGS. 4A to 4C depict explanatory views showing a process in
accordance with a second preferred embodiment of the present
invention;
[0024] FIGS. 5A and 5B are explanatory views showing the process in
accordance with the first preferred embodiment of the present
invention;
[0025] FIGS. 6A to 6C offer explanatory views showing a process in
a comparative example;
[0026] FIGS. 7A to 7C are explanatory views showing states of
patterns formed in Examples 1, 2 and the comparative example,
respectively;
[0027] FIG. 8 is an explanatory view showing the states of the
patterns formed in Examples 1, 2 and the comparative example,
respectively;
[0028] FIG. 9 is a table indicating results of a test for verifying
a shape of the pattern and powers applied to electrodes in the
etching apparatus; and
[0029] FIGS. 10A and 10B are cross-sectional views of patterns
formed in accordance with a conventional etching method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Hereinafter, there will be described preferred embodiments
of an etching method in accordance with the present invention, but
an example of an etching apparatus used in executing the etching
method will be first described with reference to FIG. 1. The
etching apparatus shown in FIG. 1 includes, for example, a
processing chamber 21 having a sealed inner space whose surface is
alumite-treated; a mounting table 3 disposed at a lower central
portion in the processing chamber 21; and an upper electrode 4
provided above the mounting table 3 to face it.
[0031] The processing chamber 21 is electrically grounded, and a
gas exhaust unit 23 is connected via a gas exhaust line 24 to a gas
exhaust port 22 formed in the bottom surface of the processing
chamber 21. The gas exhaust unit 23 includes a pressure control
part (not shown) which receives a control signal from a controller
2A to be described later, the gas exhaust unit 23 controlling the
pressure in the processing chamber 21 to be kept at a vacuum level
by evacuating the inside of the processing chamber 21 in response
to the control signal. In FIG. 1, reference numeral 25 indicates a
transfer opening for an object to be processed formed in a sidewall
of the processing chamber 21, the transfer opening 25 is closed and
opened by a gate valve 26 which is openable/closable.
[0032] The mounting table 3 includes a lower electrode 31 and a
supporting body 32 supporting the bottom surface of the lower
electrode 31, and disposed on a bottom portion of the processing
chamber 21 via an insulation member 33. An electrostatic chuck 34
is provided on the mounting table 3, and a wafer W is mounted on
the mounting table 3 via the electrostatic chuck 34. The
electrostatic chuck 34 is made of an insulating material, and an
electrode plate 36 is embedded in the electrostatic chuck 34, the
electrode plate 36 being connected to a high voltage DC power
supply. The electrostatic chuck 34 electrostatically adsorbs the
wafer W by an electrostatic force generated on the surface of the
electrostatic chuck 34 by a DC voltage applied from the DC power
supply 35 to the electrode plate 36. The electrostatic chuck 34 is
provided with through-holes 34a through which a backside gas is
discharged toward above of the electrostatic chuck 34.
[0033] A coolant path 37 is formed in the mounting table 3, and a
predetermined coolant (e.g., a known fluorine-based fluid, a water
and the like) flows through the coolant path 37 to cool the
mounting table 3 and hence the object mounted on the mounting table
3 to a desired temperature. A temperature sensor (not shown) is
installed at the lower electrode 31, temperature of the object on
the lower electrode 31 is monitored in all the way by the
temperature sensor.
[0034] Further, a gas channel 38 is formed in the mounting table 3,
and a thermally conductive gas such as He gas is supplied through
the gas channel 38 as the backside gas. The gas channel is opened
at plural locations on the top surface of the mounting table 3.
These opening portions communicate with the through-holes 34a
formed in the electrostatic chuck 34, so that the backside gas
supplied into the gas channel 38 flows through the through-holes
34a to be discharged toward above of the electrostatic chuck 34.
The backside gas is uniformly diffused throughout a gap between the
electrostatic chuck 34 and the object mounted thereon, thereby
increasing the thermal conductivity in the gap.
[0035] The lower electrode 31 is grounded via a high pass filter
(HPF) 3a, and a high frequency power supply 31a of, e.g., 13.56 MHz
is connected to the lower electrode 31 via a matching unit 31b. A
focus ring 39 is disposed on a peripheral portion of the lower
electrode 31 to surround the electrostatic chuck 34, so that a
generated plasma is focused toward the object on the mounting table
3 by the focus ring 39.
[0036] The upper electrode 4 is formed to have an inner space, and
the bottom surface thereof is provided with a plurality of holes 41
through which a processing gas is dispersedly supplied into the
processing chamber 21 to form a gas shower head. Further, a gas
introduction line 42 is connected to a central portion of the top
surface of the upper electrode 4, the gas introduction line 42
passing through the central portion of the upper wall of the
processing chamber 21 via an insulation member 27. The upstream
side of the gas introduction line 42 is divided into five branch
lines 42A to 42E ends of which are respectively connected to a
CF.sub.4 (carbon tetrafluoride) gas supply source 45A, a CH.sub.3F
(methyl fluoride) gas supply source 45B, an O.sub.2 (oxygen) gas
supply source 45C, an Ar (argon) gas supply source 45D and a
CHF.sub.3 (methane trifluoride) gas supply source 45E. In the
respective branch lines 42A to 42E, valves 43A to 43E and mass flow
controllers 44A to 44E are installed sequentially toward the
upstream side. The valves 43a to 43E and the mass flow controllers
44A to 44E constitute a gas supply system 46, and the gas supply
system controls the supplies and the flow rates of the respective
processing gases from the gas supply sources 45A to 45E in response
to the control signal from the controller 2A to be described
later.
[0037] The upper electrode 4 is also grounded via a low pass filter
(LPF) 47, a high frequency power supply 4a of, e.g., 60 MHz greater
than that of the lower electrode 31 is connected to the upper
electrode 4 via a matching unit 4b. Although not shown, the high
frequency power supplies 4a, 31 are connected to the controller 2A
and the powers applied from the high frequency power supplies to
the respective electrodes are controlled by the control signals
from the controller 2A.
[0038] In such an etching apparatus 2, the predetermined processing
gases are supplied at predetermined flow rates into the processing
chamber 21 from the processing gas supply sources 45A to 45E,
respectively, while the processing chamber 21 is evacuated by the
gas exhaust unit 23. Under such state, when the high frequency
powers are respectively applied to the lower electrode 31 and the
upper electrode 4, the processing gases are plasmarized (activated)
in the processing chamber 21 by the high frequency power applied to
the upper electrode 4 and a bias potential is generated on the
wafer W by the high frequency power applied to the lower electrode
31, so that ion species are drawn to the object to increase
verticality in the etching pattern. In this way, a desired etching
process or oxidizing process is performed on the object mounted on
the mounting table 3.
[0039] Further, the etching apparatus 2 includes the controller 2A
having, e.g., a computer. The controller 2a is provided with a data
processing unit having a program, a memory and a CPU. The program
has commands by which the controller 2A sends control signals to
each part of the etching apparatus 2 to perform each step to form a
pattern in the object. Further, the memory is provided with areas
wherein parameters such as a processing pressure, a processing
time, gas flow rates, powers and the like are recorded. The
processing parameters are read out when the CPU executes the
commands of the program, and control signals corresponding to the
parameters are transmitted to the respective parts of the etching
apparatus 2. The program (including a program related to a screen
for inputting the processing parameters) is stored in a
computer-readable storage medium such as a flexible disc, a compact
disc, a MO (magneto-optical disc) and the like and installed into
the controller 2A.
[0040] Hereinafter, there will be described an etching method in
accordance with a first preferred embodiment of the present
invention, which employs the etching apparatus 2 described above.
First, the gate valve 26 is opened, and a wafer W as a substrate is
loaded into the processing chamber 2 by a transfer mechanism (not
shown). After the wafer W is horizontally mounted on the mounting
table 3, the transfer mechanism is retreated from the processing
chamber 21 and the gate valve 26 is closed. Subsequently, a
backside gas is supplied from the gas channel 38 to increase the
thermal conductivity between the wafer W and the electrostatic
chuck 34, thereby cooling the wafer W to a predetermined
temperature. Thereafter the following steps are conducted, but the
wafer W will be described first. The materials of the films are
represented by chemical symbols for the easy correspondence to the
drawings. The wafer W is of a laminated structure as shown in FIG.
2A, wherein a SiO.sub.2 film 52, a SiN film 53 and a SiON film 54
are laminated on a Si layer 51 and a resist film 55 as an organic
film comprised mainly of an organic substance is formed on the SiON
film 54. A resist pattern 56 is formed in the resist film 55.
[0041] The SiON film 54 functions as a hard mask when the SiN film
53 is etched as will be described later, and also as a bottom
antireflection coating when the resist film 55 is exposed in a
process of forming the resist pattern 56. The thicknesses of the
SiON film 54, the SiN film 53 and the SiO.sub.2 film 52 are, e.g.,
50 nm or less, 50 nm or greater and 5 nm or less, respectively.
First Embodiment of the Etching Method of the Present Invention
[0042] (Step 1: Etching of SiON Film 54)
[0043] A gaseous mixture of CHF.sub.3 gas, CF.sub.4 gas and Ar gas
whose flow rates are controlled is supplied into the processing
chamber 21 while the gas exhaust unit 23 evacuates the inside of
the processing chamber 21 through the gas exhaust line 24 to
maintain the pressure in the processing chamber 21 to a
predetermined level. Subsequently, the high frequency powers from
the high frequency power supplies 4a, 31a are respectively applied
to the upper electrode 4 and the lower electrode 31 to plasmarize
the respective processing gases. In this way, the SiON film 54 is
etched in the resist pattern 56 by using the resist film 55 as a
mask to form a mask pattern 57, as shown in FIG. 2A.
[0044] (Step 2: Ashing of Resist Film 55)
[0045] The high frequency power supplies 4a, 31a are set OFF to
stop the generation of the plasma and, at the same time, the supply
of the CHF.sub.3 gas, the CF.sub.4 gas and the Ar gas into the
processing chamber 21 is stopped. The remaining gas in the
processing chamber 21 is exhausted by the gas exhaust unit 23 and
O.sub.2 gas is then supplied into the processing chamber 21. After
the gaseous mixture used at the step 1 in the processing chamber 21
is substituted by the O.sub.2 gas, the O.sub.2 gas is plasmarized
by applying the predetermined high frequency powers to the upper
electrode 4 and the lower electrode, respectively. With this
plasmarization, the resist film 55 ramining on the SiON film 54 is
ashed to be removed (FIG. 2C). In this ashing process, the flow
rate of the O.sub.2 gas is 300 sccm and the powers applied to the
upper and the lower electrode 4 and 31 are 300 W and 100 W,
respectively, for example.
[0046] (Step 3 Forming of Precursory Pattern 58)
[0047] The high frequency power supplies 4a, 31a are set OFF to
stop the generation of the plasma and, at the same time, the supply
of the O.sub.2 gas. The remaining O.sub.2 gas in the processing
chamber 21 is exhausted and the CHF.sub.3 gas, the CF.sub.4 gas and
the Ar gas are supplied into the processing chamber 21 at
respective controlled flow rates. After the O.sub.2 gas is
substituted by the gaseous mixture of the CHF.sub.3 gas, the
CF.sub.4 gas and the Ar gas, the gaseous mixture is plasmarized by
applying the predetermined high frequency powers to the upper
electrode 4 and the lower electrode, respectively. With this
plasmarization, a main etching of the SiN film 53 is conducted by
using the SiON film 54 as a mask to form a precursory pattern 58 of
the SiN film 53. In this etching process, in order to secure a
vertical shape and suppress any damage to the SiON film 54, the
etching is conducted under the condition of the selectivity of the
SiN film 53 to the SiO.sub.2 film 52 (etching rate of the SiN film
53/etching rate of the SiO.sub.2 film 52) of, e.g., 1 to 3.
[0048] Further, in the step 3, since the CF.sub.4 gas as a CF-based
gas is used as a part of the processing gases, the etching is
performed while polymer components are attached to sidewalls of the
precursory pattern 58 as a protective film due to active species of
the CF.sub.4 gas. Therefore, the sidewalls of the precursory
pattern 58 are formed with a high verticality, so that the shape of
a finally formed pattern 59 is controlled to form recesses with a
high verticality.
[0049] In the step 3, in order to prevent the SiO.sub.2 film 52
from being etched, the main etching process is stopped in the state
that the bottom of the precursory pattern 58 remains in the SiN
film 53, i.e., the main etching process is stopped immediately
before the SiO.sub.2 film 52, which is the underlying film of the
SiN film 53, is exposed throughout the entire surface of the wafer
W.
[0050] The overetching, in step 5 which will be described later, is
conducted under a higher selectivity of the SiN film 53 to the
SiO.sub.2 film 52 than that in the step 3, so that the sidewall
protective function of the pattern during the etching cannot be
expected compared with the step 3. Further, as the time period of
the overetching conducted in the step 5 becomes longer, the damage
to the SiON film 53 becomes greater. In this connection, it is
preferable to form the precursory pattern 58 up to a deeper
location in the SiN film 53. Further, in consideration of the
difference of the etching rate in surface, it is preferable to form
the precursory pattern 58 up to, e.g., a depth corresponding to 85%
of the thickness of the SiN film 53 on average.
[0051] (Step 4: Oxidization of SiON Film 54)
[0052] The high frequency power supplies 4a, 31a are set OFF to
stop the generation of the plasma and, at the same time, the supply
of the CHF.sub.3 gas, the CF.sub.4 gas and the Ar gas into the
processing chamber 21 is stopped. The remaining gas in the
processing chamber 21 is exhausted by the gas exhaust unit 23 and
O.sub.2 gas is then supplied into the processing chamber 21. After
the gaseous mixture used at the step 1 in the processing chamber 21
is substituted by the O.sub.2 gas, the O.sub.2 gas is plasmarized
by applying the predetermined high frequency powers to the upper
electrode 4 and the lower electrode, respectively, to thereby
oxidize the SiON film 54. In this oxidizing process, the flow rate
of the O.sub.2 gas is 1200 sccm and the powers applied to the upper
and the lower electrode 4 and 31 are 300-1500 W and 50-200 W,
respectively, for example, and the oxidizing process is conducted
under different conditions from those in the ashing process in the
step 3.
[0053] FIG. 3B shows the wafer W after the completion of the
oxidization, wherein the surface of the SiON film 54 is oxidized by
the plasma processing with the O.sub.2 gas. Reference numeral 54a
is an oxidization layer formed by oxidizing the SiON film 54. The
step 4 is conducted so as to enhance the selectivity of the SiN
film 53 to the SiON film 54 upon the overetching in the step 5,
i.e., to protect the SiON film 54 by increasing the resistance of
the SiON film 54 upon the overetching. In the step 4, it is
preferable that one to several tens of atom layers of the surface
of the SiON film 54 are oxidized. If the oxidizing process is
excessively conducted, the surface oxidization of the precursory
pattern 58 is progressed, so that the etching at the step 5 may not
be normally conducted, which would affect the formation of the
pattern 59.
[0054] (Step 5: Formation of Pattern 59)
[0055] The high frequency power supplies 4a, 31a are set OFF to
stop the generation of the plasma. Further, the remaining gas in
the processing chamber 21 is exhausted and the O.sub.2 gas, the
CHF.sub.3 gas and the Ar gas are supplied into the processing
chamber 21 at respective controlled flow rates. After the remaining
gas in the processing chamber 21 is substituted by the gaseous
mixture of the above processing gases, the gaseous mixture is
plasmarized by applying the predetermined high frequency powers to
the upper electrode 4 and the lower electrode, respectively. In
this way, the SiN film 53 remaining in the main etching process at
the step 3 is etched to form the pattern 59 by etching
(overetching) the SiO.sub.2 film 52 only for a time period during
which the SiN film 53 is surely removed throughout the entire
surface.
[0056] In this step 5, in order to suppress the SiO.sub.2 film 52
from being etched, the reaction is conducted under a higher
selectivity of the SiN film 53 to the SiO.sub.2 film 52 than that
in the step 3. Specifically, the etching is conducted under the
condition that the processing gases are supplied into the
processing chamber 21 at a ratio of the CH.sub.3F gas to the
O.sub.2 gas of 4 to 9 and the selectivity becomes, e.g., 20 or
greater.
[0057] In the etching method of the first embodiment as described
above, the main etching is conducted on the SiN film 53 by using
the SiON film 54 as the hard mask immediately before the underlying
SiO.sub.2 film 52 is exposed to thereby form the precursory pattern
58, the surface of the SiON film 54 is oxidized, and the
overetching is conducted to etch the remaining portion of the SiN
film 53 to expose the SiO.sub.2 film 52. The overetching process is
conducted under a high selectivity of the SiN film 53 to the
SiO.sub.2 film 52 since the underlying SiO.sub.2 film 52 is
extremely thin, so that a large etching action is exerted on the
SiON film 54 as the hard mask whose components are similar to those
of the SiN film 53. However, the SiON film 54 is oxidized to have a
protective film formed thereon, and the most of the SiN film 53 is
removed by the main etching to make the overetching time shorten;
and, therefore, the damage to the SiON film 54 upon the overetching
is suppressed and the generation of pitting is prevented. As a
result, it is possible to suppress the damage to the surface of the
SiN film 53. Accordingly, the pattern 59 can be formed in a good
state with respect to the laminated structure with the thin resist
film 55.
[0058] Further, although there is used, as the hard mask upon the
etching of the SiN film, a film whose principal component is a
silicon oxide, e.g., the SiON film in this embodiment, the present
invention is not limited to the SiON film and a SiOC film or a
SiCOH film may be used as the hard mask.
Second Embodiment of the Etching Method of the Present
Invention
[0059] Hereinafter, a second preferred embodiment of the present
invention will be described with reference to FIGS. 4A and 5B.
First, as shown in FIG. 4A, a wafer W having the same laminated
structure as in the first embodiment is loaded into te processing
chamber 21, and a gaseous mixture of CHF.sub.3 gas, CF.sub.4 gas
and Ar gas is supplied into the processing chamber 21. An etching
of the SiON film 54 and a main etching of the SiN film 53 are
conducted by using the resist film 55 as a mask as shown in FIG. 4B
to form the mask pattern 57 and the precursory pattern 58. The main
etching is stopped immediately before the SiO.sub.2 film is exposed
as similarly to the step 3 in the first embodiment and, therefore,
the bottom of the precursory pattern 58 lies in the SiN film
53.
[0060] Subsequently, the ashing removal of the remaining resist
film 55 is performed as similarly to the step 2 in the first
embodiment (FIG. 4C), the surface of the SiON film 54 is oxidized
to form the oxidization layer 54a as similarly to the step 4 of the
first embodiment (FIG. 5A), and the remaining SiN film 53 in the
precursory pattern 58 is overetched up to reach the SiO.sub.2 film
52 to form the pattern 59 as similarly to the step 5 of the first
embodiment (FIG. 5B).
[0061] In this embodiment, since the surface of the SiON film 54 as
the hard mask is oxidized before the overetching, the damage to the
SiON film 54 upon the overetching is suppressed and the generation
of the pitting in the SiON film 54 is prevented. Therefore, there
can be obtained the same effects as those in the first
embodiment.
[0062] Further, alternatively, the steps 4 and 3 in the first
embodiment may be exchanged. That is, after the resist film 55 on
the SiON film 54 is removed by the ashing as shown in FIG. 2C, the
surface of the SiON film 54 is oxidized as described above and the
main etching is then conducted thereon.
EXAMPLES
Example 1
[0063] In Example 1, the pattern 59 was formed on a wafer W having
the laminated structure as described in the aforementioned
embodiments in accordance with the steps in the first embodiment by
using the above-described etching apparatus 2. In Example 1, the
conditions in each step are as follows:
[0064] (Step 1: Etching of the SiON Film 54)
[0065] Pressure of the gaseous mixture: 20-50 mTorr (2.67-6.67
Pa)
[0066] Powers of the high frequency power supplies (U/L): 300-600
W/0-400 W (where, U and L represent the upper and the lower
electrode, respectively)
[0067] Flow rate ratio of the gaseous mixture:
CHF.sub.3/CF.sub.4/Ar=0-200/200-400/600 sccm
[0068] (Step 2: Ashing of the Resist Film 55)
[0069] Pressure of the O.sub.2 gas: 200 mTorr (26.7 Pa)
[0070] Powers of the high frequency power supplies (U/L): 300 W/100
w
[0071] Flow rate of the O.sub.2 gas: 300 sccm
[0072] (Step 3: Formation of Precursory Pattern 58)
[0073] Pressure of the gaseous mixture: 20-50 mTorr (2.67-6.67
Pa)
[0074] Powers of the high frequency power supplies (U/L): 300-600
W/0-400 W
[0075] Flow rate ratio of the gaseous mixture:
CHF.sub.3/CF.sub.4/Ar=0-200/200-400/600 sccm
[0076] (Step 4: Oxidization of the SiON Film 54)
[0077] Pressure of the O.sub.2 gas: 200 mTorr (26.7 Pa)
[0078] Powers of the high frequency power supplies (U/L): 300-1500
W/50-200 W
[0079] Flow rate of the O.sub.2 gas: 1200 sccm
[0080] (Step 5: Formation of the Pattern 59)
[0081] Pressure of the gaseous mixture: 120 mTorr (16.0 Pa)
[0082] Powers of the high frequency power supplies (U/L): 500
W/100-300 W
[0083] Flow rate ratio of the gaseous mixture:
CHF.sub.3/O.sub.2/Ar=3/13/90 sccm
Example 2
[0084] In Example 1, the pattern 59 was formed on a wafer W having
the same structure as that of the wafer W used in Example 1 in
accordance with the steps in the second embodiment by using the
above-described etching apparatus 2. In Example 2, the first
process of etching the SiON film 54 and the SiN film 53 by using
the resist film 55 as the mask was conducted under the following
conditions:
[0085] Pressure of the gaseous mixture: 20-50 mTorr (2.67-6.67
Pa)
[0086] Powers of the high frequency power supplies (U/L): 300-600
W/0-400 W
[0087] Flow rate ratio of the gaseous mixture:
CHF.sub.3/CF.sub.4/Ar=0-200/200-400/600 sccm
[0088] The ashing process of the resist film 55, the oxidizing
process of the SiON film 54 and the overetching process of SiN film
53, which are subsequent to the above first process, were
sequentially conducted under the same reaction conditions as those
in the steps 2, 4 and 5 in Example 1, respectively.
Comparative Example
[0089] In the comparative example, the etching process was
performed on a wafer W having the same structure as that of the
wafer used in Examples 1 and 2, as shown in FIGS. 6A to 6C. That
is, in the same way as that shown in FIG. 2 of the first
embodiment, the SiON film 54 is etched and the resist film 55 is
then ashed (FIG. 6A). Subsequently, the SiON film 54 is oxidized in
the same way as that shown in FIG. 3B, and a so-called high
selectivity etching is performed on the SiN film 53 under the
overetching conditions, so that the SiN film 53 is removed to form
the pattern 59 (FIG. 6C). The reaction conditions of each step in
the comparative example were identical to those of each step in
Example 1.
[0090] FIGS. 7A to 7C and 8 schematically show the patterns 59
formed in Examples 1, 2 and the comparative example. The schematic
diagrams were illustrated based on the results of observing the
surfaces of the processed wafers by using a scanning electron
microscope. FIG. 7A corresponds to Example 1, wherein the sidewall
of the pattern 59 was formed substantially vertically. FIG. 7B
corresponds to Example 2, wherein there were observed some
residuals 61 of the resist scattered on the bottom of the pattern
59 formed, but the amount of residuals 61 was not problematic.
Further, in Example 2, the sidewall of the pattern 59 was formed
substantially vertically. FIG. 7C corresponds to the comparative
example, wherein the pattern 59 was formed in a taper shape and
large residuals 62 such as a frog were present on the bottom of the
pattern 59. It is believed that the sidewall of the pattern 59 was
formed in the taper shape since the pattern 59 was formed under the
condition of obtaining a high selectivity for the SiO.sub.2 film 52
without forming the precursory pattern 58 and the protective action
of the polymer attachment for the sidewall was weaker than in
Examples 1 and 2. Further, it is believed that the residuals 62
appeared since, when the SiON film 54 was oxidized, the surface of
the SiN film 53, which was exposed along with the SiON film 54, was
also oxidized and the oxidized portion became a thin mask to
deteriorate the etching of the SiN film 53 in the etching under the
high selectivity condition, thereby resulting in the residuals.
Consequently, as can be seen from Examples 1, 2 and the comparative
example, in accordance with the etching method of the present
invention, the sidewall of the pattern 59 can be formed
substantially vertically and the occurrence of the residuals can be
suppressed.
[0091] Furthermore, FIG. 8 shows a cross-sectional side view and a
top view of the pattern in Examples 1, 2 and the comparative
example at the upper and the lower section, respectively. In
Examples 1 and 2, no pitting appeared in the SiON film 54, whereas
the pitting appeared in the comparative example so that holes 71
are formed to extend through the SiON film 54 to reach the SiN film
53 as shown in FIG. 8. It is believed that this is because the
precursory pattern 58 was not formed in the comparative example and
the time period of the etching performed under the high selectivity
condition for the SiN film 53 was longer than in Examples 1 and 2,
thereby resulting in an increased damage to the SiON film 54.
Consequently, it has been proved from Examples 1, 2 and the
comparative example that the etching method of the present
invention is effective for suppressing the damage exerted to the
SiON film 54 and preventing the occurrence of the pitting.
[0092] Subsequently, with respect to the oxidizing process of the
SiON film 54 in the process of forming the pattern 59, there was
executed a test for verifying the relationship between the powers
applied to the upper electrode 4 and the lower electrode 31 and the
pattern formed by oxidizing the SiON film 54 while varying the
powers. As the sequence of forming the pattern 59 in this verifying
test, there were executed the substantially same steps as those in
Example 1, but the process of etching the SiON film 54 to form the
mask pattern 57 was executed in two stages. Specifically, an
etching was first executed under a low selectivity condition for
the SiN film 53 by using the resist film 55 as a mask and an
overetching was then executed under a high selectivity condition
for the SiN film 53 by using the resist film 55 as a mask.
Thereafter, the reactions were progressed in the same steps 2 to 5
as those in the embodiment described above and an ashing was again
executed for removing a small amount of the attached polymer due to
the etching after the step 5 had been completed.
[0093] Although there has been employed, as the etching apparatus
for etching the SiON film 54 under the high selectivity condition,
the etching apparatus having the substantially same configuration
as that of the etching apparatus 2 described above, the
corresponding etching apparatus includes, as the processing gas
supply source, an additional gas supply source for C.sub.4F.sub.8
(octafluorocyclobutane) gas as a CF-based gas besides the gas
supply sources 45A to 45E provided in the etching apparatus 2, and
is configured to supply the C.sub.4F.sub.8 gas at a predetermined
flow rate into the processing chamber 21 through a mass flow
controller and a valve as similarly to the other processing
gases.
[0094] The reaction conditions in each step are as follows:
[0095] The first step (the step of etching the SiON film 54 under a
low selectivity condition for the SiN film 53)
[0096] Pressure of the gaseous mixture: 20-50 mTorr (2.67-6.67
Pa)
[0097] Powers of the high frequency power supplies (U/L): 300-600
W/0-400 W
[0098] Flow rate ratio of the gaseous mixture:
CHF.sub.3/CF.sub.4/Ar=0-200/200-400/600 sccm
[0099] The second step (the step of etching the SiON film 54 under
a high selectivity condition for the SiN film 53)
[0100] Pressure of the gaseous mixture: 50-100 mTorr (6.67-13.3
Pa)
[0101] Powers of the high frequency power supplies (U/L): 100 W/500
W
[0102] Flow rate ratio of the gaseous mixture:
C.sub.4F.sub.8/Ar/O.sub.2=0-50/800/0-50 sccm
[0103] The third step (corresponding to the step 3 in the first
embodiment)
[0104] Pressure of the O.sub.2 gas: 200 mTorr (26.7 Pa)
[0105] Powers of the high frequency power supplies (U/L): 300 W/100
w
[0106] Flow rate of the O.sub.2 gas: 300 sccm
[0107] The fourth step (corresponding to the step 3 in the first
embodiment)
[0108] Pressure of the gaseous mixture: 20-50 mTorr (2.67-6.67
Pa)
[0109] Powers of the high frequency power supplies (U/L): 300-600
W/0-400 W
[0110] Flow rate ratio of the gaseous mixture:
CHF.sub.3/CF.sub.4/Ar=0-200/200-400/600 sccm
[0111] The fifth step (corresponding to the step 4 in the first
embodiment)
[0112] Pressure of the O.sub.2 gas: 200 mTorr (26.7 Pa)
[0113] Powers of the high frequency power supplies (U/L): 300-1500
W/50-200 W
[0114] Flow rate of the O.sub.2 gas: 1200 sccm
[0115] The sixth step (corresponding to the step 5 in the first
embodiment)
[0116] Pressure of the gaseous mixture: 120 mTorr (16.0 Pa)
[0117] Powers of the high frequency power supplies (U/L): 500
W/100-300 W
[0118] Flow rate ratio of the gaseous mixture:
CHF.sub.3/O.sub.2/Ar=3/13/90 sccm
[0119] The seventh step (the step of removing a small amount of
polymer attached due to the etching)
[0120] Pressure of the O.sub.2 gas: 200 mTorr (26.7 Pa)
[0121] Powers of the high frequency power supplies (U/L): 300 W/100
w
[0122] Flow rate of the O.sub.2 gas: 1200 sccm
[0123] FIG. 9 shows the results of the above steps. In FIG. 9, the
vertical and the horizontal axes of the left table represent the
powers applied to the upper and the lower electrode 4 and 31 in the
fifth step, respectively, and the numbers in the table indicate
.theta. shown in the right of the FIG. 9, i.e., the angle of the
sidewall of the pattern 59 formed to the horizontal plane. As can
be seen from FIG. 9, as the power applied to the lower electrode 31
is decreased compared with the power applied to the upper electrode
4 to reduce the attraction of O.sub.2 plasma toward the precursory
pattern 58, .theta. becomes closer to 90.degree., thereby resulting
in a good pattern shape.
[0124] While the invention has been shown and described with
respect to the preferred embodiment, it will be understood by those
skilled in the art that various changes and modifications may be
made without departing from the scope of the invention as defined
in the following claims.
* * * * *